This invention relates generally to friction clutches, and has particular reference to a novel self-adjusting clutch cover assembly that automatically compensates for friction disc facing wear.
In friction type clutches, the driven disc or discs are disengaged from the driving flywheel and pressure plate by actuation of the release levers which are in turn actuated by axial movement of the release mechanism. Movement of the release mechanism is normally effected by a yoke member connected through a linkage to the clutch pedal of the vehicle. In engaged condition, the clutch driving and driven members are urged into engagement by pressure springs and as wear occurs on the clutch disc facings, these springs move the pressure plate closer to the flywheel.
The inward movement of the pressure plate results in a force which tends to change the normal position of the associated release levers and release mechanism and thereby to change the adjustment required for proper operation. Thus, if the free ends of the levers and the release mechanism move inwardly with the pressure plate, this may cause binding between the release bearing and yoke member or at some other point. If, on the other hand, the release mechanism is held against inward movement, binding may occur between the lever ends and spider portion of the release mechanism.
One solution to this problem has been periodic manual adjustment of the release mechanism to compensate for wear. In one type of clutch, this is accomplished by changing the angle of the yoke member. In another type, the release lever spider includes a sleeve threadedly mounted on one end of a second sleeve having the release bearing mounted on its opposite end. This permits relative axial movement between the sleeves whereby the distance between the release lever ends and yoke member can be changed to compensate for wear. A release mechanism having manual adjustment means of this last-mentioned type is disclosed in U.S. Pat. No. 2,863,537 to Root, owned by the assignee of the present invention.
Another solution to this problem has been a self-adjusting clutch release mechanism such as disclosed in U.S. Pat. No. 3,433,341 issued to Bohn et al. This construction includes a release mechanism with a collapsible or extendable release bearing carrier permitting the repositioning of the release bearing with respect to the friction discs.
Both the manual and the self-adjusting constructions compensate for the wear by repositioning the release mechanism but neither takes into consideration the gradually increasing distance between the pressure plate and the clutch cover. Thus, as the pressure plate moves axially to compensate for wear on the friction discs there is a general change in the operation of the clutch. For example, the release levers move through a changed angle resulting in a changed distance through which the yoke must be pulled for disengagement. Also, the distance through which the pressure springs must act is increased resulting in a change in torque and a change in the force needed to effect disengagement.